Light emitting device with bonded interface

ABSTRACT

In some embodiments of the invention, a transparent substrate AlInGaP device includes an etch stop layer that may be less absorbing than a conventional etch stop layer. In some embodiments of the invention, a transparent substrate AlInGaP device includes a bonded interface that may be configured to give a lower forward voltage than a conventional bonded interface. Reducing the absorption and/or the forward voltage in a device may improve the efficiency of the device.

BACKGROUND

1. Field of Invention

The present invention relates to a semiconductor light emitting devicewith a doped wafer-bonded interface and/or a less absorbing etch stoplayer.

2. Description of Related Art

Light emitting diodes (LEDs) are widely accepted as light sources inmany applications that require low power consumption, small size, andhigh reliability. Energy-efficient diodes that emit light in theyellow-green to red regions of the visible spectrum contain activelayers formed of an AlGaInP alloy. FIGS. 1A-1B and 2A-2B show thefabrication of a conventional transparent substrate (TS) AlGaInP LED. InFIGS. 1A-1B, an etch stop layer 12 such as a 1000 Å n-In_(0.5)Ga_(0.5)Player, is grown over a semiconductor substrate 10, typically GaAs.Device layers 14, including a lower confining layer, at least one(Al_(x)Ga_(1-x))_(y)In_(1-y)P active layer, and an upper confininglayer, all placed in a double heterostructure configuration, are grownover etch stop layer 12, followed by an optional thick (for example,between 5 and 100 μm thick) window layer 16, often p-type GaP grown byvapor phase epitaxy. The confining layers are made of a transparentsemiconductor and enhance the internal quantum efficiency of the LED,defined as the fraction of electron-hole pairs in the active layer thatrecombine and emit light. The window layer 16, also a transparentsemiconductor, increases the spread of electric current across theactive layer and enhances the internal quantum efficiency of the diode.The light emitting region may consist of a single thick uniformcomposition layer or a series of thin wells and barriers.

GaAs is preferred as a growth substrate because it is lattice matched to(Al_(x)Ga_(1-x))_(y)In_(1-y)P at compositions favored for the formationof LEDs that emit light in the yellow-green to red regions of thevisible spectrum, at y˜0.5. Since GaAs is absorbing, it is typicallyremoved and replaced by a transparent substrate 18, as illustrated inFIGS. 2A-2B. GaAs substrate 10, shown in FIGS. 1A-1B, is removed by anetch that etches GaAs at a much faster rate than etch stop layer 12. Atransparent substrate 18, typically n-type GaP, is wafer bonded to thelower surface of the epitaxial structure (etch stop layer 12 in FIGS.2A-2B), generally by annealing the structure at an elevated temperaturewhile uniaxial force is applied. LED chips are then processed from thebonded wafers using conventional metal contacts and chip fabricationtechniques suitable for the p-type epitaxial GaP anode and the n-typewafer-bonded GaP cathode.

SUMMARY

In some embodiments of the invention, a transparent substrate AlInGaPdevice includes an etch stop layer that may be less absorbing than aconventional etch stop layer. In some embodiments of the invention, atransparent substrate AlInGaP device includes a bonded interface thatmay be configured to give a lower forward voltage than a conventionalbonded interface. Reducing the absorption and/or the forward voltage ina device may improve the efficiency of the device.

In some embodiments, a light emitting device includes a firstsemiconductor structure comprising an AlGaInP light emitting layerdisposed between an n-type region and a p-type region, and a secondsemiconductor structure. A bond formed at an interface disposed betweenthe first and second semiconductor structures connects the firstsemiconductor structure to the second semiconductor structure. At leastone semiconductor layer at the interface is doped to a concentration ofat least 2×10¹⁸ cm⁻³. Increasing the dopant concentration at the bondedinterface may reduce the forward voltage of the device.

In some embodiments, a light emitting device is formed by growing afirst semiconductor structure on a GaAs substrate. The firstsemiconductor structure includes an etch stop layer with a thicknessless than 150 Å and an AlGaInP light emitting layer disposed between ann-type region and p-type region. The GaAs substrate is removed, then thefirst semiconductor structure is bonded to a second semiconductorstructure. The etch stop layer may be InGaP or AlGaInP, and may or maynot be lattice-matched to GaAs. Reducing the thickness and/or changingthe bandgap of the etch stop layer may reduce absorption by the etchstop layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate a prior art A1GaInP LED device structure grownover an absorbing substrate.

FIGS. 2A-2B illustrate a prior art transparent substrate AlGaInP LED.

FIGS. 3A-3B illustrate a transparent substrate AlGaInP LED with an etchstop layer that is less absorbing than a conventional etch stop layer.

FIGS. 4A-4B illustrate a transparent substrate AlGaInP LED with animproved wafer bonded interface.

It is desired to maximize the wall plug efficiency (WPE), defined as theratio of light extracted from a device to electrical power supplied tothe device, of AlGaInP LEDs. Embodiments of the invention attempt toimprove the wall plug efficiency of an AlGaInP LED by improving theoptical and/or electrical characteristics of the bonded interfacebetween the epitaxial device structure and the transparent substrate.

One method of increasing the light output of AlGaInP LEDs is to decreasethe absorption of light within the device. One source of absorption isInGaP etch stop layer 12 of FIGS. 2A-2B. Since InGaP has a more narrowbandgap than the AlGaInP light emitting region, etch stop layer 12 willabsorb some of the light emitted by the light emitting region.

FIGS. 3A-3B illustrates a device with a less-absorbing etch stop layer20. The fabrication of the device illustrated in FIGS. 3A-3B is similarto the device illustrated in FIGS. 2A-2B. Etch stop layer 20 is grownover an absorbing substrate, followed by device layers 14 and optionalthick window layer 16. The absorbing substrate is removed, and theremaining structure is wafer-bonded to a transparent substrate 18.Contacts are formed on the wafer-bonded structure, then individual LEDsare diced.

In some embodiments, etch stop layer 20 is InGaP that is lattice matchedto the GaAs growth substrate as in a conventional etch stop layer, butis formed thinner than a conventional InGaP etch stop layer and is thusless absorbing than a thick etch stop layer. For example, an InGaP etchstop layer 20 may have a thickness less than 250 Å, more preferably lessthan 150 Å, and more preferably less than 130 Å.

In some embodiments, etch stop layer 20 is a material that has a largerband gap, and is thus more transparent, than In_(0.5)Ga_(0.5)P. The bandgap may be increased by increasing the amount of aluminum in the etchstop layer, or by decreasing the amount of indium in the etch stoplayer. For example, etch stop layer 20 may be a quaternary AlGaInP or aternary InGaP layer with a larger band gap than In_(0.5)Ga_(0.5)P. In anAlGaInP or InGaP etch stop layer 20, the InP composition may be lessthan 50%, preferably between 40 and 50%. The AlP composition in anAlGaInP layer may be between 0 and 50%, with the optimal AlP compositiondepending on LED configuration. For example, in a configuration whereelectrical current is passed through the etch stop layer, a lower AlPcomposition is preferred, for example in the range from 0% AlP to 10%AlP, where 10% AlP refers to the alloy(Al_(0.20)Ga_(0.80))_(0.5)In_(0.5)P. Alternatively, in a configurationwhere electrical current is not pa through the etch stop layer, a higherAlP composition is preferred, for example in the range from 10% AlP to20% AlP, where 20% AlP refers to the alloy(Al_(0.40)Ga_(0.60))_(0.5)In_(0.5)P.

Larger band gap etch stop layer 20 mayor may not be lattice-matched tothe GaAs growth substrate. Band gap energy may be plotted as a functionof lattice constant for binary, ternary, and quaternary alloys of AI,In, Ga, and P. InGaP layers with an InP composition less than 50% arenot lattice-matched to GaAs. Quaternary AlInGaP layers with acomposition (AlxGal-x)o.5Ino.5P, are lattice-matched to GaAs. Otherquaternary alloys but with a higher band gap than lattice-matched InGaP,may be suitable as etch stop layer 20.

For example, a quaternary etch stop layer of(Al_(0.10)Ga_(0.90))_(0.5)In_(0.5)P could be used for an LED configuredto emit light in the red region of the visible spectrum with a dominantwavelength ≧620 nm. In such a case, the thickness of the quaternary etchstop layer is preferably ≦500 Å, more preferably ≦250 Å, and morepreferably ≦150 Å. Alternatively, a non-zero AlP composition may becombined with a lower InP composition to make a more transparent layer,such as (Al_(0.10)Ga_(0.90))_(0.55)In_(0.45)P. For LEDs configured toemit shorter wavelength light, such as yellow or amber light, a higherAlP composition may be preferred, such as(Al_(0.15)Ga_(0.85))_(0.5)In_(0.5)P, or(Al_(0.15)Ga_(0.85))_(0.55)In_(0.45)P. Etch stop layers with AlPcompositions as high as (Al_(0.30)Ga_(0.70))_(0.5)In_(0.5)P have beenshown to work, although in some examples of such LEDs with(Al_(0.30)Ga_(0.70))_(0.5)In_(0.5)P etch stop layers, the LED V_(f) hasbeen observed to increase, possibly due to oxidation of the high AlPcomposition layers that are exposed to air, to the ambient in the hightemperature wafer bonding process, or to the etch stop layer etchingsolution. One method of decreasing internal absorption while avoidingthis high V_(f) may be to slowly increase the AlP composition of theetch stop layer, either in a series of discrete steps, or in acontinuous ramp. Alternatively, in the event that this etch stop layeris not used as an electrical contact layer, oxidation at this etch stoplayer is not a problem, and even higher AlP compositions can be used,such as (Al_(0.40)Ga_(0.60))_(0.5)In_(0.5)P or(Al_(0.40)Ga_(0.60))_(0.55)In_(0.45)P, with no V_(f) penalty.

The emission spectrum of an LED is given approximately by FWHM≈1.8 kT,where FWHM is the full width at half maximum of the LED emissionspectrum measured in eV, k is Boltzman's constant, and T is the LEDtemperature in Kelvin. To minimize internal absorption within the etchstop layer, the bandgap of the etch stop layer should thus be increasedto a value of at least approximately 1.8 kT above the bandgap energy ofthe active layer. Since room temperature corresponds to roughly 25 meV,and since a biased LED will heat up above room temperature, in someembodiments the bandgap of the etch stop layer is increased to a valueof at least 50 meV above the bandgap of the active layer, usingincreased AlP composition or decreased InP composition, or both.

In devices where the light emitting layer emits long wavelength light,such as red and red-orange light, the AlP composition in the lightemitting layer is low enough that etch stop layer 20 may be madetransparent. For example, an LED configured to emit red light may havean active layer composition of (Al_(0.05)Ga_(0.95))_(0.5)In_(0.5)P. Insuch a case, the etch stop layer may be made transparent by using anetch stop layer with compositions such as(Al_(0.15)Ga_(0.85))_(0.5)In_(0.5)P or(Al_(0.10)Ga_(0.90))_(0.55)In_(0.45)P. In such cases where the etch stoplayer is transparent, the thickness of the etch stop layer is limited bystrain and the Matthews-Blakeslee critical thickness, so thicker etchstop layers may be used, up to for example 500 Å thick. In some cases itmay be impractical to increase the bandgap of the etch stop layer morethan 50 meV above the active layer bandgap, so a compromise between theconventional etch stop layer 12 in FIGS. 1A-1B and the transparent etchstop layer described above may be preferred. For example, an etch stoplayer with bandgap equal to or slightly greater than the active layerbandgap may be preferred in some case, while in other cases, an etchstop layer with bandgap=active layer bandgap+kT≈active layerbandgap+0.025 eV or an etch stop layer with bandgap=active layerbandgap+2 kT≈active layer bandgap+0.050 eV may be preferred.

A lattice-mismatched etch stop layer may be thin. In general, the largerthe lattice mismatch, the thinner the layer should be in order to avoidstrain relaxation. For example, an etch stop layer composed of(Al_(x)Ga_(1-x))_(0.60)In_(0.40)P grown on GaAs should be kept below athickness of approximately 300 Å, while an etch stop layer composed of(Al_(x)Ga_(1-x))_(0.55)In_(0.45)P grown on GaAs should be kept below athickness of approximately 800 Å to avoid strain relaxation. Thinneretch stop layers of these compositions may be preferred to avoidabsorption if these compositions are not transparent to light emitted bythe active layer. For example, a lattice-mismatched etch stop layer 20may be less than 250 Å thick, more preferably less than 150 Å, and morepreferably less than 130 Å.

The addition of AlP to a lattice-matched or lattice-mismatched etch stoplayer may increase the temperature at which the etch stop layer isgrown, which may favorably suppress the incorporation of oxygenimpurities in the etch stop layer.

In some embodiments, multiple etch stop layers are included in thedevice. Multiple etch stop layers may be separated from each other byGaAs layers, though they need not be. At least one of these multipleetch stop layers may be composed of phosphide layers, such as InGaP orAlInGaP, while one or more other etch stop layers may be composed ofarsenide layers such as AlGaAs. The device layers are grown over thelast etch stop layer. Any of the etch stop layers described in theembodiments above may be used in a device with multiple etch stoplayers. The etch stop layers in a device may each have the sameproperties (such as composition and thickness), though they need not. Ina first example, a first InGaP etch stop layer is grown over a GaAssubstrate, followed by a layer of GaAs, followed by a second InGaP etchstop layer. In a second example, an AlGaAs first etch stop layer isgrown over a GaAs substrate, followed by an InGaP second etch stoplayer. In a third example, an AlGaAs first etch stop layer is grown overa GaAs substrate, followed by an AlInGaP second etch stop layer.

Any of the above-described approaches, either individually, or inarbitrary combinations, may decrease internal absorption and thereforeincrease LED light output or WPE.

Another method of increasing the WPE of AlGaInP LEDs is to reduce theforward voltage V_(f) of the device. One source of increased V_(f) in awafer-bonded transparent substrate AlGaInP LED is the wafer bondedinterface between the transparent GaP substrate 18 and the AlGaInPdevice layers 14, which may contain incomplete “dangling” bonds, orimpurities such as carbon, oxygen, or organic or inorganic compoundsassociated with the crystal growth, etching, and wafer bondingprocesses.

These dangling bonds or impurities typically create electronic defectstates at or near the wafer-bonded interface that hinder carriertransport across the interface. One method of decreasing the effect ofthese defect states on V_(f) is to dope the region at or near thewafer-bonded interface, as illustrated in FIGS. 4A-4B. In the device ofFIGS. 4A-4B, device layers 14 are bonded to transparent substrate 18 byan interface between etch stop layer 20, grown with device layers 14,and an InGaP bonding layer 22, grown on transparent substrate 18. InGaPbonding layer 22 may have an InP composition between, for example, 0%and 50%, more preferably between 5% and 30%, and more preferably between8% and 16%. In a conventional device, the layers forming the bondedinterface are typically doped to a dopant concentration of approximately1×10¹⁸ cm⁻³. In the device illustrated in FIGS. 4A-4B, the dopantconcentration in one or both of bonding layer 22 and etch stop layer 20is at least 2×10¹⁸ cm⁻³, more preferably at least 5×10¹⁸ cm⁻³, and morepreferably at least 7×10¹⁸ cm⁻³, up to, for example, 2×10¹⁹ cm⁻³. In apreferred embodiment, the dopant is Te, though Si, S, or any othersuitable dopant including p-type dopants may be used. The preferreddoping levels may be higher when using a dopant such as Si, which istypically not fully activated. In addition, the optimum InP compositionin bonding layer 22 may be higher, since the smaller Si atoms do not addadditional strain to the lattice.

Device layers 14 include a light emitting region sandwiched between ann-type region and a p-type region. The light emitting region includes atleast one light emitting layer, which is often undoped. In someembodiments, one or both of etch stop layer 20 and bonding layer 22 aremore heavily doped than one or both of the n-type region and the p-typeregion.

On the top side of the bonded interface illustrated in FIGS. 4A-4B, etchstop layer 20 may be a conventional thick InGaP layer that islattice-matched to GaAs, or an etch stop layer or layers according toembodiments of the invention, as described above. In the prior artdevice illustrated in FIGS. 1A-1B, an In GaP etch stop layer 12 is grownon a GaAs buffer layer which is grown on a GaAs substrate 10. Thetransition from GaAs to InGaP or to (Al_(x)Ga_(1-x))_(y)In_(1-y)Prequires the gas phase chemistry to be changed from AsH3 in the GaAslayers to PH3 in the InGaP or (Al_(x)Ga_(1-x))_(y)In_(1-y)P layers, anda growth pause is typically used for this AsH₃ to PH₃ switchingsequence. In some embodiments of the invention, the dopant source flowis left on during this growth pause in order to increase the dopantconcentration in etch stop layer 20. The surface of the wafer is thuspre-purged with dopant as growth of the etch stop layer begins, whichmay increase the dopant concentration in etch stop layer 20. In someembodiments, the flow of PH₃ is reduced during growth of etch stop layer20. In such cases, the PH₃ flow used during growth of etch stop layer 20may be less than that used to grow device layers 14. For example, insome embodiments, the PH₃ flow used to grow etch stop layer 20 may beonly 80% of the lowest PH₃ flow used to grow device layers 14. In otherembodiments, the PH₃ flow used to grow layer 20 may be only 50% of thelowest PH₃ flow used to grow device layers 14.

On the bottom side of the bonded interface illustrated in FIGS. 4A-4B isbonding layer 22. Transparent substrate 18 is composed of GaP andbonding layer 22 is composed of In_(x)Ga_(1-x)P, where x is typicallybetween 0% and 50%, more preferably between 5% and 30%, and morepreferably between 8% and 16%. Since x is typically not 0%, bondinglayer 22 is not lattice matched to the GaP substrate 18, and InGaPbonding layer 22 is grown to a thickness that typically is in the rangefrom 0.5× to 3× the Matthews-Blakeslee critical thickness for strainrelaxation. If relaxed, the InGaP bonding layer 22 typically has a mildcross hatch on the wafer surface, with a peak to valley surfaceroughness −5 to 15 nm, and an RMS roughness −2 to 3 nm in a 1 O×10 or50×50 μm atomic force microscope image.

High doping in the bonding layer is conventionally achieved byincreasing the dopant source flow. In the case of large dopant atomssuch as Te, there is a significant competition between the incorporationof large dopant atoms such as Te and the incorporation of large matrixelement atoms such as indium into the smaller GaP crystal lattice. Thiscompetition creates a feedback loop between Te suppression and indiumsuppression in InGaP bonding layer 22. Maintaining the desired InPcomposition while simultaneously increasing the Te doping concentrationrequires the use of higher Te doping source flow, but the higher Tedoping source flow suppresses indium incorporation and reduces InPcomposition, which requires the use of higher indium source flow. Thishigher indium source flow in turn suppresses Te incorporation andrequires even higher Te doping source flow, which in turn requires evenhigher indium source flow. This competition often results in either toolittle InP in bonding layer 22, or too much InP in bonding layer 22,thus making it difficult to reproducibly grow a bonding layer of thedesired thickness, InP composition, and dopant concentration. Too muchInP can lead to the onset of a three dimensional island growth modewhich gives a surface that is too rough, and often results in films thatare highly defective and non-conducting, producing an LED with highV_(f). Too little InP can result in a poor quality bond, and bubbles atthe bonded interface. Since InP has a weaker bond strength than GaP, thepresence of InP at the wafer bonded interface allows for more atomicre-arrangement at the wafer bonded interface during wafer bonding, andthus improves the bond between transparent substrate 18 and etch stoplayer 20. A minimum amount of InP is therefore preferred at the bondedinterface.

In some embodiments of the invention, InGaP bonding layer 22 is grown toa thickness where bonding layer 22 relaxes enough to permit moreincorporation of dopant. For example, bonding layer 22 may be grown to athickness greater than 3000 Å thick, more preferably between 5,000 and20,000 Å, and more preferably between 5,000 and 10,000 Å, which mayexceed the Matthews-Blakeslee critical thickness by as much as 3× ormore. As the thickness of bonding layer 22 increases, the surfaceroughness typically increases, for example to a peak to valley surfaceroughness ˜15 nm to ˜50 nm or more, and RMS roughness of 3 nm to 6 nm ormore. The rough surface and reduced strain may decrease the competitionbetween In and Te incorporation in the bonding layer, and maysubstantially decouple the interaction between In and Te incorporationinto the bonding layer, permitting the incorporation of more Te for agiven Te doping source flow. This decoupling of the Te and Inincorporation may result in a more reproducible manufacturing process.In some embodiments, bonding layer 22 is grown thick enough to begin tosubstantially relax, and a constant doping source flow is used duringgrowth of InGaP bonding layer 22, resulting in a dopant concentrationthat naturally increases for a fixed doping source flow rate. In otherembodiments, a fixed dopant source flow is used until the InGaP bondinglayer 22 substantially relaxes, then a higher dopant source flow is usedto further increase the dopant concentration in the film withoutsubstantially decreasing the indium composition in the film, or withoutincreasing the indium source flow. In such an embodiment, the dopingconcentration in the film can be increased to greater than 1×10¹⁹ cm⁻³,while maintaining the InP composition in bonding layer 22 to within 0.5%of the target value, with no change in indium source flow. In someembodiments, at least a part of the InGaP bonding layer is doped to aconcentration of at least 5×10¹⁸ cm⁻³.

The increased surface roughness of bonding layer 22 may also increasethe wafer bonding yield by decreasing bubbles at the wafer-bondedinterface, in contrast to Hoshi, who teaches in U.S. Pat. No. 5,196,375that smoother surfaces with peak to valley roughness <13 nm arepreferred for low bubble density in wafer-bonded layers.

In a first example of a TS AlGaInP device according to embodiments ofthe invention, the etch stop layer is conventional, for example, InGaPlattice-matched to GaAs grown to a thickness greater than 250 Å. Bondinglayer 22 is InGaP with an InP composition between 0% and 50%, morepreferably between 5% and 30%, and more preferably between 8% and 16%,grown to a thickness greater than 700 Å, and doped with Te to aconcentration of 8×10¹⁸ cm⁻³. The V_(f) of such a device has beenobserved to be less than the V_(f) of a conventional device.

In a second example of a TS AlGaInP device according to embodiments ofthe invention, the etch stop layer is conventional, for example, InGaPlattice-matched to GaAs grown to a thickness greater than 250 Å. Bondinglayer 22 is InGaP with an InP composition between 0% and 50%, morepreferably between 5% and 30%, and more preferably between 8% and 16%,grown to a thickness between 2,000 and 20,000 Å, and doped with Te to aconcentration of 8×10¹⁸ cm⁻³. The V_(f) of such a device has beenobserved to be less than the V_(f) of a conventional device.

In a third example, etch stop layer 20 is InGaP lattice-matched to GaAs,grown to a thickness less than 150 Å and doped with Te to aconcentration less than 10¹⁸ cm⁻³, according to embodiments of theinvention. Bonding layer 22 is InGaP with an InP composition between 0%and 50%, more preferably between 5% and 30%, and more preferably between8% and 16%, grown to a thickness between 2,000 and 20,000 Å, and dopedwith Te to a concentration of 8×10¹⁸ cm⁻³. The V_(f) of such a devicehas been observed to be about the same as the V_(f) of a conventionaldevice, though the device has higher light output than a conventionaldevice.

In a fourth example, etch stop layer 20 is AlGaInP lattice-mismatched toGaAs, grown thin enough to avoid strain relaxation, with, for example, acomposition of (Al_(0.10)Ga_(0.90))_(0.55)In_(0.45)P and a thicknessless than 500 Å, doped with Te to a concentration greater than 2×10¹⁸cm⁻³. Bonding layer 22 is InGaP with an InP composition between 0% and50%, more preferably between 5% and 30%, and more preferably between 8%and 16%, grown to a thickness between 2,000 and 20,000 Å, and doped withTe to a concentration of 8×10¹⁸ cm⁻³.

In a fifth example, the active layer is In_(1-y)Ga_(y)P with0.45≦y≦0.55, and etch stop layer 20 is AlGaInP lattice-mismatched toGaAs, grown thin enough to avoid strain relaxation, with, for example, acomposition of (Al_(0.10)Ga_(0.90))_(0.55)In_(0.45)P and a thicknessless than 500 Å, doped with Te to a concentration greater than 5×10¹⁷cm⁻³. Bonding layer 22 is InGaP with an InP composition between 8% and16%, grown to a thickness between 800 and 20,000 Å, and doped with Te toa concentration greater than 1×10¹⁸ cm⁻³.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcept described herein. For example, though the embodiments describedherein are III-P light emitting diodes, it is to be understood thatother devices, such as lasers, and other materials systems are withinthe scope of the invention. Therefore, it is not intended that the scopeof the invention be limited to the specific embodiments illustrated anddescribed.

What is being claimed is:
 1. A device comprising: a first semiconductorstructure comprising an AlGaInP light emitting layer disposed between ann-type region and a p-type region; a second semiconductor structure; anda direct semiconductor-to-semiconductor bond formed at an interfacebetween the first and second semiconductor structures; wherein: the bondconnects the first semiconductor structure to the second semiconductorstructure; a first semiconductor layer adjacent to the interface is anInGaP layer between 5,000 and 10,000 Å thick that is doped with Te to aconcentration of at least 5×10¹⁸ cm⁻³; and a second semiconductor layeradjacent to the interface is an InGaP layer less than 250 Å thick anddoped with Te.
 2. The device of claim 1, wherein at least one of thefirst and second semiconductor layers adjacent to the interface isroughened wherein the maximum to minimum excursion of the roughness isgreater than 15 nm.
 3. The device of claim 1, wherein at least one ofthe first and second semiconductor layers adjacent to the interface hasa bulk lattice constant different from a bulk lattice constant of GaAs.4. The device of claim 3 wherein at least one of the first and secondsemiconductor layers adjacent to the interface with the bulk latticeconstant different from a bulk lattice constant of GaAs is one of InGaPand AlGaInP.
 5. The device of claim 1, wherein at least one of the firstand second semiconductor layers adjacent to the interface has a gradedcomposition.
 6. The device of claim 1, wherein a band gap of at leastone of the first and second semiconductor layers adjacent to theinterface is greater than a band gap of the light emitting layer.
 7. Thedevice of claim 1, wherein a band gap of at least one of the firstsemiconductor layers adjacent to the interface is greater than a bandgap of the light emitting layer plus 0.025 eV.
 8. The device of claim 1,wherein the second semiconductor structure comprises a transparent GaPlayer at least 10 μm thick.
 9. The device of claim 1, wherein at leastone of the first and second semiconductor layers adjacent to theinterface is more heavily doped than at least one of the p-type regionand the n-type region.
 10. A device comprising: a first semiconductorstructure comprising an AlGaInP light emitting layer disposed between ann-type region and a p-type region; a second semiconductor structure; anda direct semiconductor-to-semiconductor bond formed at an interfacebetween the first and second semiconductor structures; wherein: the bondconnects the first semiconductor structure to the second semiconductorstructure; and a first semiconductor layer adjacent to the interface isAlGaInP with a thickness less than 500 Å and doped with Te to aconcentration greater than 2×10¹⁸ cm⁻³; and a second semiconductor layeradjacent to the interface is InGaP with an InP composition between 8%and 16%, with a thickness between 2,000 and 20,000 Å, and doped with Teto a concentration of 8×10¹⁸ cm⁻³.
 11. The device of claim 10, whereinat least one of the first and second semiconductor layers adjacent tothe interface is roughened wherein the maximum to minimum excursion ofthe roughness is greater than 15 nm.
 12. The device of claim 10, whereinat least one of the first and second semiconductor layers adjacent tothe interface has a bulk lattice constant different from a bulk latticeconstant of GaAs.
 13. The device of claim 12 wherein at least one of thefirst and second semiconductor layers adjacent to the interface with thebulk lattice constant different from a bulk lattice constant of GaAs isone of InGaP and AlGaInP.
 14. The device of claim 10, wherein at leastone of the first and second semiconductor layers adjacent to theinterface has a graded composition.
 15. The device of claim 10, whereina band gap of at least one of the first and second semiconductor layersadjacent to the interface is greater than a band gap of the lightemitting layer.
 16. The device of claim 10, wherein a band gap of atleast one of the first semiconductor layers adjacent to the interface isgreater than a band gap of the light emitting layer plus 0.025 eV. 17.The device of claim 10, wherein the second semiconductor structurecomprises a transparent GaP layer at least 10 μm thick.
 18. The deviceof claim 10, wherein at least one of the first and second semiconductorlayers adjacent to the interface is more heavily doped than at least oneof the p-type region and the n-type region.